Magnetic recording media are widely used in audio tapes, video tapes, computer tapes, disks and the like. Magnetic media may use thin metal layers as the recording layers, or may comprise coatings containing magnetic particles as the recording layer. The former type of recording media employs metals such as cobalt, cobalt chrome, cobalt nickel, cobalt chrome platinum, and other cobalt alloys. The latter type of recording media employs particulate materials such as ferromagnetic iron oxides, chromium oxides, ferromagnetic alloy powders and the like dispersed in binders and coated on a substrate. In general terms, magnetic recording media generally comprise a magnetic layer coated onto at least one side of a non-magnetic substrate.
In media based on a thin metallic magnetic recording layer, such as a magnetic cobalt alloy, the overall media construction will generally include several thin films coated in sequence which form a “thin film stack.” The first thin film stack layers coated generally function to provide a combination of adhesion, topographical texture, and crystalline texture. These layers are then followed by one or more magnetic thin films which do the actual information storage. The magnetic thin films are followed by one or more coatings which provide environmental stability, hardness, and compatibility with the subsequently coated lube. The lube layer constitutes the final layer of the thin film media.
Optical recording media, such as magneto-optical disks, store information on a thin film of magneto-optical material disposed between two protective layers. The basic principal of operation is to use a laser to locally raise the temperature of the magneto-optical layer to near the Curie point and switch the direction of the local magnetization to the direction of a recording magnetic field applied to the disk. The two protective layers enclose the magneto-optical material to protect it from corrosion, and are formed from materials such as silicon nitride, silicon oxide, or aluminum nitride dielectrics. The read/write head of a recording mechanism glides above the disk surface. Lubricants are disposed on the surface to protect both the disk head and the disk surface from damage. The lubricants reduce friction between the disk head and surface and they enhance the wear resistance of the disk.
Lubricants useful for both types of recording media have been organic lubricants such as fatty acid esters, silicones, and perfluoropolyesters such as polytetrafluoro-ethylene (PTFE). However, conventional lubricants may degrade when exposed to high temperatures forming sludge on the surface, and migration of the lubricants due to centrifugal force depletes the lubricant from the surface of the disk. Optical media make particularly high demands on lubricants due to the high local temperatures caused by the laser beam. Such temperatures can reach as high as 350° C. Many conventional lubricants begin to degrade or vaporize at temperatures of from 165° C. to 300° C., depending on the functional end group and the molecular weight, reducing the amount available.
It would be useful to have a lubricant which would remain stable at temperatures exceeding 350° C., and which would bond to the surface of the recording medium, reducing migration and transfer to the recording head. It has now been discovered that a functionalized perfluoropolyether comprising multiple acrylate endgroups increases thermal stability and percentage of bonded lubricant percentage.